SQL：如何在联接中使用CASE

Question

这是我正在尝试使用的代码

SELECT
  TData.dtContractDate,
  TData.chPurchase,
  TData.nShipperID,
  TData.nSourceSiteId,
  Vendor.chShipperName,
  Vendor.chCity,
  Vendor.chState,
  Vendor.chCountry,
  Vendor.chZip 
FROM Data1.dbo.TData TData
JOIN Data1.dbo.Vendor
  ON Vendor.nShipperId = TData.nShipperID
  AND Vendor.nCompanyCode  = (CASE WHEN Vendor.nCompanyCode = '2' THEN '2' ELSE '26' END)
WHERE (TData.nCompanyCode=2) AND (TData.dtContractDate > '" 04/23/2015 12:01:00 AM')

我正在尝试加入这两个表，但是如果

ncompanycode = 2 AND Vendor.nShipperId = TData.nShipperID ，

那我想拉那些数据，如果这个不存在，那我想用

ncompanycode = 26 and Vendor.nShipperId = TData.nShipperID 。

现在，我得到了两家公司拥有的所有shipperID副本。

这是虚拟表以及我得到的结果，我不希望chPurchase重复。

TData表

|            dtContractDate | chPurchase | nShipperID | nSourceSiteId | nCompanyCode |
|---------------------------|------------|------------|---------------|--------------|
| January, 04 2015 00:00:00 |    2547635 |        453 |      68686868 |            2 |
| January, 05 2015 00:00:00 |    2547636 |        453 |      68686868 |            2 |
| January, 06 2015 00:00:00 |    2547637 |        454 |      68686868 |            2 |
| January, 07 2015 00:00:00 |    2547638 |        454 |      68686868 |            2 |
| January, 08 2015 00:00:00 |    2547639 |        455 |      68686868 |            2 |
| January, 09 2015 00:00:00 |    2547640 |        456 |      68686868 |            2 |

供应商表

| nCompanyCode | nShipperID | chShipperName | chCity | chState | chCountry |  chZip |
|--------------|------------|---------------|--------|---------|-----------|--------|
|            2 |        453 |         Name1 | Dallas |      TX |        US | 666555 |
|           26 |        453 |         Name2 | Dallas |      TX |        US | 666556 |
|            2 |        454 |         Name3 | Dallas |      TX |        US | 666557 |
|           26 |        455 |         Name4 | Dallas |      TX |        US | 666558 |
|            2 |        455 |         Name5 | Dallas |      TX |        US | 666559 |
|           26 |        456 |         Name6 | Dallas |      TX |        US | 666560 |

结果表

|   dtContractDate | chPurchase | nShipperID | nSourceSiteId | nCompanyCode | chShipperName | chCity | chState | chCountry |  chZip |
|------------------|------------|------------|---------------|--------------|---------------|--------|---------|-----------|--------|
| January, 04 2015 |    2547635 |        453 |      68686868 |           26 |         Name2 | Dallas |      TX |        US | 666555 |
| January, 04 2015 |    2547635 |        453 |      68686868 |            2 |         Name1 | Dallas |      TX |        US | 666555 |
| January, 05 2015 |    2547636 |        453 |      68686868 |           26 |         Name1 | Dallas |      TX |        US | 666556 |
| January, 05 2015 |    2547636 |        453 |      68686868 |            2 |         Name2 | Dallas |      TX |        US | 666556 |
| January, 06 2015 |    2547637 |        454 |      68686868 |            2 |         Name3 | Dallas |      TX |        US | 666557 |
| January, 07 2015 |    2547638 |        454 |      68686868 |            2 |         Name3 | Dallas |      TX |        US | 666558 |
| January, 08 2015 |    2547639 |        455 |      68686868 |            2 |         Name5 | Dallas |      TX |        US | 666559 |
| January, 08 2015 |    2547639 |        455 |      68686868 |           26 |         Name5 | Dallas |      TX |        US | 666559 |
| January, 09 2015 |    2547640 |        456 |      68686868 |            26 |         Name6 | Dallas |      TX |        US | 666560 |

Answer 1

此解决方案不使用CASE但使用COALESCE在更干净的条件下产生期望的结果。

为了缩短可读性，我已经缩短了表别名。

我还注释了涉及日期的WHERE子句，因为：

1. 格式不正确，不会与当前错别字匹配任何日期。
2. 纠正错别字后，它将消除样本数据中的所有行。

SQL代码使用两个LEFT JOINs并使用COALESCE选择在SELECT输出中使用哪个。 当第一个JOIN （ V ）结果为NULL ，输出求助于V2 。 V2 JOIN明确要求nCompanyCode为26 ，但是如果存在多个替代nCompanyCodes则可以根据需要添加或删除任何条件。

查询：

SELECT
   T.dtContractDate
  ,T.chPurchase
  ,T.nShipperID
  ,T.nSourceSiteId
  ,COALESCE(V.chShipperName,V2.chShipperName) chShipperName
  ,COALESCE(V.chCity,V2.chCity) chCity
  ,COALESCE(V.chState, V2.chState) chState
  ,COALESCE(V.chCountry,V2.chCountry) chCountry
  ,COALESCE(V.chZip,V2.chZip) chZip
  -- Added to show what Vendor company code is being used
  ,COALESCE(V.nCompanyCode,V2.nCompanyCode) nCompanyCode
FROM TData T
LEFT JOIN Vendor V
  ON V.nShipperId = T.nShipperID
  AND V.nCompanyCode = T.nCompanyCode
LEFT JOIN Vendor V2
  ON V2.nShipperId = T.nShipperID
  AND V2.nCompanyCode <> T.nCompanyCode
  AND V2.nCompanyCode = 26
-- Commented out this WHERE clause because it eliminates all rows
-- WHERE T.dtContractDate > '04/23/2015 12:01:00 AM'

样本输出：

|   dtContractDate | chPurchase | nShipperID | nSourceSiteId | chShipperName | chCity | chState | chCountry |  chZip | nCompanyCode |
|------------------|------------|------------|---------------|---------------|--------|---------|-----------|--------|--------------|
| January, 04 2015 |    2547635 |        453 |      68686868 |         Name1 | Dallas |      TX |        US | 666555 |            2 |
| January, 05 2015 |    2547636 |        453 |      68686868 |         Name1 | Dallas |      TX |        US | 666555 |            2 |
| January, 06 2015 |    2547637 |        454 |      68686868 |         Name3 | Dallas |      TX |        US | 666557 |            2 |
| January, 07 2015 |    2547638 |        454 |      68686868 |         Name3 | Dallas |      TX |        US | 666557 |            2 |
| January, 08 2015 |    2547639 |        455 |      68686868 |         Name5 | Dallas |      TX |        US | 666559 |            2 |
| January, 09 2015 |    2547640 |        456 |      68686868 |         Name6 | Dallas |      TX |        US | 666560 |           26 |

你可以用SQLFiddle在这个例子中发挥这里 。

Answer 2

我认为您想要的是将两个托运人ID相等的表连接起来，然后从该集合中选择公司代码等于您想要的值的所有行。 另外，似乎您不希望WHERE (TData.nCompanyCode=2)条件，因为您已经在尝试选择公司代码在2或26以上的位置。 尝试这个：

SELECT TData.dtContractDate, TData.chPurchase, TData.nShipperID, 
TData.nSourceSiteId,  Vendor.chShipperName, Vendor.chCity,     
Vendor.chState,  Vendor.chCountry, Vendor.chZip 
FROM Data1.dbo.TData TData
Join Data1.dbo.Vendor on Vendor.nShipperId = TData.nShipperID
WHERE Vendor.nCompanyCode  = (case when Vendor.nCompanyCode = '2' then     
'2' else '26' end)
AND (TData.dtContractDate > '" 04/23/2015     
12:01:00 AM')